I use the internal memory and two cards. Folder are Artists\Album\Tracks. All FLAC. Also had CBR MP3 for a bit to test some things. The issue that does exist for me is VBR MP3 get their last 2s cut off. The AK literally thinks the song is 2s shorter than it is. 3:14 becomes 3:12 on the duration bar. But shuffle works. My files were ripped with JRiver and converted a bunch with dBpoweramp to create a replay gain set for the AK.